1. Field of the Invention
This invention relates to a focusing device of a binocular in which an interpupillary adjustment is carried out by a biaxial interlock mechanism.
2. Description of the Related Art
Conventionally, a binocular is provided with an interpupillary adjustment function. The distance between the eyes of different users of binocular varies, by carrying out the interpupillary adjustment function, a distance between optical axes of a pair of eyepieces can be adjusted to suit the distance between the eyes of any user. There is a biaxial type binocular, as a binocular having the interpupillary adjustment function.
In the biaxial type binocular, telescopic optical stems have respective Porro prisms as erector prismatic systems, respective objective optical systems and respective eyepieces whose optical axes are displaced out of alignment with those of the objective optical systems. Each of a pair of eyepieces and Porro prisms are respectively rotated around an optical axis of a corresponding objective optical system of a pair of objective optical systems, and the rotations of the eyepieces are interlocked. Namely, there are two axes of rotation of the eyepieces to adjust the distance between the optical axes of the eyepieces.
On the other hand, the biaxial type binocular also has a focusing function. The focusing function is carried out by moving any optical systems of the telescopic optical systems along optical axes of the telescopic optical systems, so that an object image, formed by the objective optical systems, is brought into focus. As the eyepieces are rotatably held for the interpupillary adjustment in the above-mentioned biaxial type binocular, the focusing function is generally performed by moving the objective optical systems.
If other functions, for example a zooming and a focused image tremble correcting function, are added to the biaxial type binocular, it is advantageous that other optical systems for these other functions are situated close to the objective optical systems. It is then possible to share the same elements in order to perform different functions and to save weight and space in the binocular.
However, in the biaxial type binocular, a focusing assembly, by which the objective optical systems are held and moved along the optical axes thereof, is disposed close to the objective optical systems. Namely, it becomes difficult to unitarily install the other optical systems close to the objective optical systems, without causing enlargement of the binocular.